Arbitarary waveform generation using nanosecond pulses

ABSTRACT

Some embodiments include a high voltage waveform generator comprising: a generator inductor; a high voltage nanosecond pulser having one or more solid state switches electrically and/or inductively coupled with the generator inductor, the high voltage nanosecond pulser configured to produce a pulse burst having a burst period, the pulse burst comprising a plurality of pulses having different pulse widths; and a load electrically and/or inductively coupled with the high voltage nanosecond pulser, the generator inductor, and the generator capacitor, the voltage across the load having an output pulse with a pulse width substantially equal to the burst period and the voltage across the load varying in a manner that is substantially proportional with the pulse widths of the plurality of pulses.

BACKGROUND

Producing high voltage pulses with fast rise times and/or fast falltimes is challenging. For instance, to achieve a fast rise time and/or afast fall time (e.g., less than about 50 ns) for a high voltage pulse(e.g., greater than about 5 kV), the slope of the pulse rise and/or fallmust be incredibly steep (e.g., greater than 10¹¹ V/s). Such steep risetimes and/or fall times are very difficult to produce especially incircuits driving a load with high capacitance. Such pulses may beespecially difficult to produce using standard electrical components;and/or with pulses having variable pulse widths, voltages, andrepetition rates; and/or within applications having capacitive loadssuch as, for example, a plasma.

SUMMARY

Some embodiments may include a high voltage waveform generatorcomprising: a generator inductor; a high voltage nanosecond pulserelectrically and/or inductively coupled with the generator inductor, thehigh voltage nanosecond pulser configured to charge the generatorinductor with: a first pulse burst comprising a first plurality of highvoltage pulses, each pulse of the first plurality of pulses having apulse width, the first pulse burst having a first burst period; and asecond pulse burst comprising a second plurality of high voltage pulses,each pulse of the second plurality of pulses having a pulse width, thesecond pulse burst having a second burst period; and a plasmaelectrically coupled with the nanosecond pulser and the generatorinductor, the voltage across the plasma varying according to: a firstplasma pulse having a first output pulse width and a first outputvoltage, the first output pulse width being substantially equal to thefirst burst period and the first output voltage being substantiallyproportional to a pulse width of each of the pulses of the firstplurality of pulses, and a second plasma pulse having a second outputpulse width and a second output voltage, the second output pulse widthbeing substantially equal to the second burst period and the secondoutput voltage being substantially proportional to a pulse width of eachof the pulses of the second plurality of pulses.

In some embodiments, either or both the first pulse burst and the secondpulse burst has an amplitude greater than 500 V. In some embodiments,either or both the first plasma pulse and the second plasma pulse has anamplitude greater than 500 V.

In some embodiments, the second pulse burst has an amplitude that isdifferent than the amplitude of the first pulse burst. In someembodiments, wherein the amplitude of one or more of the first pluralityof high voltage pulses is different than amplitude of one or more of theother first plurality of high voltage pulses. In some embodiments,wherein the voltage of the first plasma pulse is different than thevoltage of the second plasma pulse.

In some embodiments, the high voltage waveform generator may include apulldown resistor electrically and/or inductively coupled with thegenerator inductor and the high voltage nanosecond pulser. In someembodiments, the high voltage waveform generator may include atransformer.

In some embodiments, the first burst period and/or the second burstperiod is less than about 50 ms. In some embodiments, either or both thefirst plasma pulse and the second plasma pulse establish a potentialwithin the plasma.

In some embodiments, either or both the first plasma pulse and thesecond plasma pulse accelerate ions within the plasma. In someembodiments, either or both the first plurality of pulses and/or thesecond plurality of pulses have a frequency greater than about 50 kHz.In some embodiments, at least one pulse of the first plurality of pulseshas a pulse width and/or at least one pulse of the second plurality ofpulses has a pulse width less than 500 ns.

In some embodiments, the generator inductor comprises stray inductance.In some embodiments, the generator inductor has an inductance less thanabout 20 μH. In some embodiments, the peak output power is greater than10 kW. In some embodiments, the plasma is substantially capacitive innature.

Some embodiments may include a high voltage waveform generatorcomprising: a generator inductor; a generator capacitor electricallyand/or inductively coupled with the generator inductor; a high voltagenanosecond pulser electrically or inductively coupled with the generatorinductor and the generator capacitor, the high voltage nanosecond pulserconfigured to charge the generator inductor with a first pulse burst anda second pulse burst; and a load electrically and/or inductively coupledwith the nanosecond pulser, the generator inductor, and the generatorcapacitor, the voltage across the load varying according to: a firstload pulse and/or a second load pulse. In some embodiments, the firstpulse burst comprises a plurality of high voltage pulses, each pulse ofthe plurality of pulses having a first pulse width and a voltage greaterthan 500 V, the first pulse burst having a first burst period; and/orthe second pulse burst may comprise a plurality of high voltage pulses,each pulse of the plurality of pulses having a second pulse width and avoltage greater than 500 V, the second pulse burst having a second burstperiod. In some embodiments, the first load pulse may have a firstoutput pulse width and a first output voltage, the first output pulsewidth being substantially equal to the first burst period and the firstoutput voltage being proportional to the first pulse width, and thesecond load pulse may have a second output pulse width and a secondoutput voltage, the second output pulse width being substantially equalto the second burst period and the second output voltage beingproportional to the second pulse width.

In some embodiments, the first pulse output voltage is greater than 500V, and the second pulse output voltage is greater than 500 V. In someembodiments, the first pulse output voltage is greater than the secondpulse output voltage. In some embodiments, the load comprises a plasma.

In some embodiments, the high voltage waveform generator may include apulldown resistor electrically and/or inductively coupled with thegenerator inductor and the high voltage nanosecond pulser. In someembodiments, the high voltage waveform generator may include atransformer. In some embodiments, the first burst period is less thanabout 1 microsecond, the first pulse width is less than about 200nanoseconds, and the second pulse width is less than about 200nanoseconds.

Some embodiments of the invention include a method for generating highvoltage waveforms. In some embodiments, the method may includegenerating a first pulse burst comprising a plurality of high voltagepulses, each pulse of the plurality of pulses having a first pulse widthand a voltage greater than 500 V, the first pulse burst having a firstburst period; charging a generator inductor with the first pulse burst;outputting a first output pulse having a first output pulse width and afirst output voltage, the first output pulse width being substantiallyequal to the first burst period and the first output voltage beingproportional to the first pulse width; generating a second pulse burstcomprising a plurality of high voltage pulses, each pulse of theplurality of pulses having a second pulse width and a voltage greaterthan 500 V, the second pulse burst having a second burst period;charging a generator inductor with the second pulse burst; andoutputting a second output pulse having a first output pulse width and asecond output voltage, the second output pulse width being substantiallyequal to the second burst period and the second output voltage beingproportional to the second pulse width.

In some embodiments, the first pulse output voltage is greater than 500V, and the second pulse output voltage is greater than 500 V. In someembodiments, the first pulse output voltage is greater than the secondpulse output voltage. In some embodiments, the first output pulse andthe second output pulse is provided to a plasma. In some embodiments,the first burst period is less than about 10 ms, the second burst periodis less than about 10 ms, the first pulse width is less than 200nanoseconds, and the second pulse width is less than 200 nanoseconds.

Some embodiments of the invention may include a high voltage waveformgenerator comprising: a generator inductor; a generator capacitorelectrically and/or inductively coupled with the generator inductor; ahigh voltage nanosecond pulser electrically and/or inductively coupledwith the generator inductor and the generator capacitor, the highvoltage nanosecond pulser configured to charge the generator inductorwith a first pulse burst and/or a second pulse burst; and a loadelectrically and/or inductively coupled with the nanosecond pulser, thegenerator inductor, and the generator capacitor, the voltage across theload varying according to a first load pulse and a second load pulse.

In some embodiments, the first pulse burst may comprise a plurality ofhigh voltage pulses having a first voltage, each pulse of the pluralityof pulses having a first pulse width and a voltage greater than 500 V,the first pulse burst having a first burst period. In some embodiments,the second pulse burst may comprise a plurality of high voltage pulseshaving a second voltage, each pulse of the plurality of pulses having asecond pulse width and a voltage greater than 500 V, the second pulseburst having a second burst period.

In some embodiments the first load pulse may have a first output pulsewidth and a first output voltage, the first output pulse width beingsubstantially equal to the first burst period and the first outputvoltage being a function of the first pulse width and/or the firstvoltage. In some embodiments, the second load pulse may have a secondoutput pulse width and a second output voltage, the second output pulsewidth being substantially equal to the second burst period and thesecond output voltage being a function of the second pulse width and/orthe second voltage.

In some embodiments, the load comprises a plasma. In some embodiments,the first burst period is less than about 10 ms, the second burst periodis less than about 10 ms, the first pulse width is less than 200nanoseconds, and the second pulse width is less than 200 nanoseconds.

Some embodiments of the invention include a high voltage waveformgenerator comprising a generator inductor; a generator capacitorelectrically and/or inductively coupled with the generator inductor; ahigh voltage nanosecond pulser having one or more solid state switcheselectrically and/or inductively coupled with the generator inductor andthe generator capacitor, the high voltage nanosecond pulser configuredto produce a pulse burst having a burst period, the pulse burstcomprising a plurality of pulses having different pulse widths; and aload electrically and/or inductively coupled with the high voltagenanosecond pulser, the generator inductor, and the generator capacitor,the voltage across the load having an output pulse with a pulse widthsubstantially equal to the burst period and the voltage across the loadvarying in a manner that is substantially proportional with the pulsewidths of the plurality of pulses.

In some embodiments, the load comprises a plasma. In some embodiments,at least a subset of the plurality of pulses have pulse widths withincreasingly larger widths and the absolute value of the voltage acrossthe load increases. In some embodiments, the pulse burst has anamplitude greater than about 500 V.

BRIEF DESCRIPTION OF THE FIGURES

These and other features, aspects, and advantages of the presentdisclosure are better understood when the following Disclosure is readwith reference to the accompanying drawings.

FIG. 1 is a block diagram of an example high voltage waveform generatoraccording to some embodiments.

FIG. 2 is a block diagram of an example high voltage waveform generatoraccording to some embodiments.

FIGS. 3A and 3B are block diagrams of example high voltage waveformgenerators according to some embodiments.

FIGS. 4A and 4B are block diagrams of example high voltage waveformgenerators according to some embodiments.

FIGS. 5A and 5B are block diagrams of example high voltage waveformgenerators according to some embodiments.

FIG. 6 is a block diagram of an example high voltage waveform generatoraccording to some embodiments.

FIG. 7 is a circuit diagrams of an example high voltage waveformgenerator according to some embodiments.

FIG. 8A illustrates an example pulser waveform and an example highvoltage waveform generator output waveform according to someembodiments.

FIG. 8B illustrates an example high voltage waveform generator outputwaveform according to some embodiments.

FIG. 8C illustrates an example pulser waveform according to someembodiments.

FIG. 8D illustrates an example high voltage waveform generator outputwaveform according to some embodiments.

FIGS. 9A and 9B illustrate an example pulser waveform and an examplehigh voltage waveform generator output waveform according to someembodiments.

FIGS. 10A and 10B illustrate an example pulser waveform and an examplehigh voltage waveform generator output waveform according to someembodiments.

FIGS. 11A and 11B illustrate an example pulser waveform and an examplehigh voltage waveform generator output waveform according to someembodiments.

FIG. 12 illustrates example waveforms within various circuit elements ofa high voltage waveform generator according to some embodiments.

FIG. 13 illustrates example waveforms within various circuit elements ofa high voltage waveform generator according to some embodiments.

FIG. 14 illustrates example waveforms within various circuit elements ofa high voltage waveform generator according to some embodiments.

FIG. 15 illustrates an example pulser waveform and an example highvoltage waveform generator output waveform according to someembodiments.

DETAILED DESCRIPTION

Systems and methods are disclosed to generate high voltage waveformswith arbitrary pulse widths, voltages, and/or shapes. In someembodiments, a high voltage waveform generator may include a pulser(e.g., a nanosecond pulser) and a generator circuit. For example, ananosecond pulser may produce a burst of high voltage pulses having aburst period T_(br) and each pulse of the burst of pulses having a pulsewidth T_(p). The generator circuit may produce an output pulse from theinput burst of high voltage pulses. The output pulse, for example, mayhave a pulse width approximately the same as the burst period T_(br).The output pulse, for example, may have a voltage that is a function of(e.g., proportional to) the pulse width T_(p) of each pulse of the burstof pulses. The output pulse, for example, may have a voltage that is afunction of (e.g., proportional to) the voltage V_(p) of the inputpulses, or the frequency of the input pulses, f_(p).

In some embodiments, the peak power of the output pulses may be greaterthan about 1 kW, 10 kW, 100 kW, 1,000 kW, 10,000 kW, etc.

In some embodiments, the pulser may produce a burst train. Each bursttrain, for example, may include a plurality of bursts and each of theplurality of bursts may include a plurality of pulses. Each burst of theplurality of bursts (e.g., N bursts) may have a burst period (e.g.,T_(br1), T_(br2), T_(br3), . . . T_(brN)). The resulting output of thehigh voltage waveform generator may include a plurality of pulse widths(e.g., PW_(br1), PW_(br2), PW_(br3), . . . PW_(brN)) proportional (e.g.,roughly equal) to each burst period. In some embodiments, the burstperiods may vary resulting in variable output pulse widths. In someembodiments, the output voltage amplitude may be proportional to thepulse width of each pulse within a burst. The voltage of each outputpulse may also be proportional to the voltage and frequency of the inputpulse burst.

FIG. 1 is a block diagram of an example high voltage waveform generator100 according to some embodiments. The high voltage waveform generator100 may include a nanosecond pulser 105 and a load 110. The nanosecondpulser 105 may be electrically and/or inductively coupled with the load110 via the diode 125, a generator inductor 115, and/or a generatorcapacitor 120. An additional inductor 116 may also be included. Theshape of the waveform across the load 110 may be set by the pulse widthof the nanosecond pulser 105 and/or the pulse frequency (or burstperiod) of the nanosecond pulser 105, and/or the pulse voltage of thenanosecond pulser 105.

In some embodiments, the additional inductor 116 may not be included. Insome embodiments, the additional inductor 116 and the generator inductor115 may not be included.

The nanosecond pulser 105, for example, may include any device capableof producing pulses greater than 500 V, peak current greater than 10Amps, and/or pulse widths of less than about 10,000 ns, 1,000 ns, 100ns, 10 ns, etc. As another example, the nanosecond pulser 105 mayproduce pulses with an amplitude greater than 1 kV, 5 kV, 10 kV, 50 kV,200 kV, etc. As another example, the nanosecond pulser 105 may alsoproduces pulse with rise times less than about 5 ns, 50 ns, or 300 ns,etc.

The nanosecond pulser 105 may, for example, include any pulser describedin U.S. patent application Ser. No. 14/542,487, titled “HIGH VOLTAGENANOSECOND PULSER”, which is incorporated into this disclosure in itsentirety for all purposes.

The nanosecond pulser 105 may, for example, include any pulser describedin U.S. Pat. No. 9,601,283, titled “EFFICIENT IGBT SWITCHING”, which isincorporated into this disclosure in its entirety for all purposes.

The nanosecond pulser 105 may, for example, include any pulser describedin U.S. patent application Ser. No. 15/365,094, titled “HIGH VOLTAGETRANSFORMER”, which is incorporated into this disclosure in its entiretyfor all purposes.

The nanosecond pulser 105 may, for example, include a high voltageswitch. For example, the nanosecond pulser 105 may, for example, includeany switch described in U.S. Patent Application Ser. No. 62/717,637,filed Aug. 10, 2018, titled “HIGH VOLTAGE SWITCH WITH ISOLATED POWER”,which is incorporated into this disclosure in its entirety for allpurposes.

In some embodiments, the nanosecond pulser 105 may include one or moresolid state switches such as, for example, an IGBT, a MOSFET, a SiCMOSFET, SiC junction transistor, FETs, SiC switches, GaN switches,photoconductive switch, etc.

In some embodiments, the generator inductor 115, for example, mayinclude any inductor having an inductance less than about 3 μH. In someembodiments, the generator inductor 115 may represent stray inductancewithin the circuit such as, for example, within leads from thenanosecond pulser to other components in the circuit, or other circuitcomponents. In some embodiments, the generator inductor 115 may have aninductance less than 1 μH, 0.1 μH, and 10 nH, 1 μH, 10 μH, 50 μH, etc.

In some embodiments, the additional inductor 116, for example, mayinclude any inductor having an inductance less than about 3 μH. In someembodiments, the additional inductor 116 may represent stray inductancewithin the circuit such as, for example, within leads from thenanosecond pulser to other components in the circuit, or other circuitcomponents. In some embodiments, the additional inductor 116 may have aninductance less than 1 μH, 0.1 μH, 10 nH, 1 μH, 10 μH, 50 μH, etc.

The generator capacitor 120, for example, may include any capacitorhaving a capacitance less than about 1 μF. For example, the generatorcapacitor 120 may have a capacitance be less than 1 μF, 10 μF, 100 nF,100 pF, etc. The generator capacitor 120 may represent stray capacitancewithin the circuit such as, for example, within the leads, or betweenother generator circuit components, or it may represent capacitancecontained within the load 110.

In this example, when the nanosecond pulser 105 is turned on andproduces a high voltage pulse (e.g., a pulse greater than about 500 V, 5kV, 10 kV, 15 kV, etc.), energy from the pulse is injected into thegenerator inductor 115. The energy from the generator inductor 115 canthen charge the generator capacitor 120. When the nanosecond pulser 105is turned off, the energy in the generator inductor 115 can continue tocharge the generator capacitor 120. If the pulse width of the highvoltage pulse is long enough to completely charge the generatorcapacitor 120, the voltage across the generator capacitor 120 can betwice the voltage of the high voltage pulse. By varying the pulse width,the frequency, and/or the voltage of the high voltage pulses, thevoltage across the generator capacitor 120 can be varied. For example,the voltage across the generator capacitor 120 may be proportional tothe pulse width, frequency, and/or voltage of the high voltage pulsefrom the nanosecond pulser 105 as shown by the waveforms shown in FIGS.8A, 8B, 8C, and 8D.

In some embodiments, the phrase “charge the inductor” can be used todescribe energy is passed through the inductor and/or energy is storedwithin the inductor.

In some embodiments, generator inductor 115 may not be used to regulatehow much energy charges the generator capacitor 120. Some energy fromthe nanosecond pulser 105 may end up in the generator inductor 115,however, much of the energy will just pass through the generatorinductor 115 into the generator capacitor 120. Thus, in someembodiments, the generator inductor 115 and/or the additional inductor116 may not be included.

FIG. 2 is a block diagram of an example high voltage waveform generator200 according to some embodiments. In this example, the load is a plasma111. The inductors 115 and/or 116 may not be present, or may consist ofjust the stray circuit inductance. The capacitance 120 may be part ofthe plasma's capacitance. The plasma may have a number of uniquecharacteristics, such as, for example, a capacitance, an electronmobility, and an ion mobility that differs from the electron mobility.In this example, output pulses of variable voltages may be applied tothe plasma 111. The plasma 111 may include any type of plasma that mayinclude charged ions and/or charged radicals. In some embodiments, theplasma may be used in a semiconductor fabrication process. In someapplications, the output pulse amplitude may be used to control theenergy of the plasma ions. In some applications, the ions may be used toetch various materials. These materials may include wafers used in themanμFacture of semiconductors. In some embodiments, the high voltagewaveform generator 200 can be used to control the voltage applied acrossa plasma 111 or a plasma sheath.

FIG. 3A is a block diagram of an example high voltage waveform generator300 according to some embodiments. In this example, the high voltagewaveform generator 300 may include a driving cable 124 such as, forexample, a coax cable or a twin lead cable.

In some embodiments, the generator capacitor 120, for example, may be inseries with the load 110 as shown by circuit 350 in FIG. 3B.

FIG. 4A is a block diagram of an example high voltage waveform generator400 according to some embodiments. In this example, the high voltagewaveform generator 400 includes a transformer 121 between the nanosecondpulser 105 and the load 110. Either the generator L and or C may bepresent, and/or C might be in series with the load 110, for example. Insome embodiments, the pulse generator 105 may also contain a transformerthat may galvanically isolate the pulser output from its input.

In some embodiments, the generator capacitor 120 may be in series withthe load 110 as shown in circuit 450 as shown in FIG. 4B.

FIG. 5A is a block diagram of an example high voltage waveform generator500 according to some embodiments. In this example, the high voltagewaveform generator 500 includes a pulldown resistor 130. A switch mayalso be included in series with the pulldown resistor 130. The pulldownresistor 130 may, for example, include any embodiment described in U.S.patent application Ser. No. 15/941,731, titled “HIGH VOLTAGE PASSIVEOUTPUT STAGE CIRCUIT”, which is incorporated into this disclosure in itsentirety for all purposes.

In some embodiments, the generator capacitor 120 may be in series withthe load 110 as shown in circuit 550 in FIG. 5B. In some embodiments,the generator capacitor 120 may be part of the load 110 and/or includeall or part of the capacitance of the load 110. In some embodiments, thepull down resistor 130 may be placed before the generator capacitor 120,the effective load capacitance 115, and/or the diode 125, i.e. placedcloser to generator 105.

FIG. 6 is a block diagram of an example high voltage waveform generator600 according to some embodiments. In this example, the high voltagewaveform generator 600 may include a load having an effective loadcapacitance 115, an effective load current generator 140, and/or aneffective load diode 142 and an effective system inductance 115. Aplasma, for example, may be idealized by the effective current generator140, the effective load diode 142, and the effective load capacitance143. In some embodiments, the effective current generator 140 canrepresent the plasma ion current. In some embodiments, the ion plasmacurrent can flow fairly steadily between the input pulses, for aroundthe duration of the output pulse. In some embodiments, the effectiveload capacitance 143 can represent the capacitance formed in the plasma.In some embodiments, effective load capacitance 115 can represent thecapacitance across the material/item/component being treated by theplasma, for example a semiconductor wafer being etched. In someembodiments, the effective load diode 142 can represent the electronmobility within the plasma, and/or the flow of current through theplasma driven by the input nanosecond pulses, that occurs around theduration of the input pulse burst.

FIG. 7 shows another example high voltage waveform generator 700according to some embodiments. The high voltage waveform generator 700can be generalized into five stages (these stages could be broken downinto other stages or generalized into fewer stages). The high voltagewaveform generator 700 includes pulser and transformer stage 706, aresistive output stage 707, a lead stage 710, a blocking capacitor andDC bias power supply stage 711, and a load stage 110.

In this example, the load stage 110 may represent an effective circuitfor a plasma deposition system, plasma etch system, or plasma sputteringsystem. In some embodiments, the capacitance of capacitor C1 and/orcapacitor C12 may be less than about 50 μF, 10 μF, 1 μF, 100 nF, etc.The capacitor C2 may represent the capacitance of the dielectricmaterial upon which a wafer may sit. In some embodiments, the capacitorC2 may be less than about 50 μF, 10 μF, 1 μF, 100 nF, etc. The capacitorC3 may represent the sheath capacitance of the plasma to the wafer. Insome embodiments, the capacitor C3 may be less than about 50 μF, 10 μF,1 μF, 100 nF, etc. The capacitor C9 may represent capacitance within theplasma between a chamber wall and the top surface of the wafer. Thecurrent source 12 and the current source I1 may represent the ioncurrent through the sheath.

In this example, the resistive output stage 707 may include one or moreinductive elements represented by inductor L1 and/or inductor L5. Theinductor L5, for example, may represent the stray inductance of theleads in the resistive output stage 707. Inductor L1 may be set tominimize the power that flows directly from the pulser and transformerstage 706 into resistor R1. In some embodiments, the resistance ofresistor R1 can be less than about 2,000 Ohms, 200 Ohms, 20 Ohms, 2Ohms, etc.

In some embodiments, the inductor L2, inductor L5, and/or inductor L6may have an inductance less than about 100 μH, 10 μH, 1 μH, 100 nH, etc.

In some embodiments, the resistor R1 may dissipate charge from the load110, for example, on fast time scales (e.g., 1 ns, 10 ns, 100 ns, 250ns, 500 ns, 1,000 ns, etc. time scales). The resistance of resistor R1may be low to ensure the pulse across the load 110 has a fast fall timet_(f).

In some embodiments, the resistor R1 may include a plurality ofresistors arranged in series and/or parallel. The capacitor C11 mayrepresent the stray capacitance of the resistor R1 including thecapacitance of the arrangement series and/or parallel resistors. Thecapacitance of stray capacitance C11, for example, may be less than 2000pF, 500 pF, 250 pF, 100 pF, 50 pF, 10 pF, 1 pF, etc. The capacitance ofstray capacitance C11, for example, may be less than the loadcapacitance such as, for example, less than the capacitance of C2, C3,and/or C9.

In some embodiments, a plurality of pulser and transformer stages 706can be ganged up in parallel and coupled with the resistive output stage707 across the inductor L1 and/or the resistor R1. Each of the pluralityof pulser and transformer stages 706 may each also include diode D1and/or diode D6. In some embodiments, the inductance of inductor L1 canbe less than about 1,000 μH, 100 μH, 10 μH, etc.

In some embodiments, the capacitor C8 may represent the straycapacitance of the blocking diode D1. In some embodiments, the capacitorC4 may represent the stray capacitance of the diode D6.

In some embodiments, the DC bias power supply stage 711 may include DC avoltage source V1 that can be used to bias the output voltage eitherpositively or negatively. In some embodiments, the capacitor C12isolates/separates the DC bias voltage from the resistive output stageand other circuit elements. The capacitor C12 may be referenced aseither a blocking capacitor and/or a bias capacitor. In someembodiments, capacitor C12 may comprise a single capacitive element, ornumerous capacitive elements combined. In some embodiments, capacitorC12 may allow for a potential shift from one portion of the circuit toanother. In some embodiments, the potential shift capacitor C12establishes may be used to hold a wafer in place using electrostaticforces. In some embodiments, the capacitance of capacitor C12 may beless than about 1000 μF, 100 μF, 10 μF, 1 μF, etc.

Resistance R2 may protect/isolate the DC bias supply from the highvoltage pulsed output from the pulser and transformer stage 706. In someembodiments, the DC bias power supply stage may contain additionalelements such as switches, diodes, and capacitors, to help keep theelectrostatic forces holding a wafer in place fairly constant in time,as the output pulse cycles on and off such as, for example, U.S. PatentApplication Ser. No. 62/711,406, filed Aug. 10, 2018, titled “NANOSECONDPULSER BIAS COMPENSATION”, which is incorporated into this disclosure inits entirety for all purposes.

In some embodiments, the pulser and transformer stage 706 may include aplurality of switches and a plurality of signal generators. A pluralityof switches, for example, may allow the nanosecond pulser to producehigher frequency pulses.

In some embodiments, the voltage source V2 provides a consistent DCvoltage that is switched by switch S1. Switch S1, for example, mayinclude one or more solid state switches such as, for example, an IGBT,a MOSFET, a SiC MOSFET, SiC junction transistor, FETs, SiC switches, GaNswitches, photoconductive switch, etc. Switch S1 may switch so fast thatthe switched voltage may never be at full voltage. For example, ifvoltage source V2 provides a DC voltage of 500 V, then the switch S1 maybe turned on and turned off so quickly that the voltage across theswitch is less than 500 V. In some embodiments, a gate resistor coupledwith the switch S1 may be set with short turn on pulses.

FIG. 8A illustrates an example pulser waveform and FIG. 8B illustratesan example high voltage waveform generator output waveform according tosome embodiments. In this example, the waveform produced by the pulserinclude two bursts: a first burst with a burst period B₁ with each pulsehaving a pulse width T₁; and a second burst with a burst period B₂ witheach pulse having a pulse width T₂. The waveform output is the output ofthe waveform generator based on the waveform produced by the pulser. Inthis example, the waveform generator outputs two pulses: a first pulsehaving a pulse width PW₁ and a voltage V₁; and a second pulse having apulse width PW₂ and a voltage V₂. In this example, the PW₁ is the samelength as the burst period B₁ within 10%; and the first pulse voltage V₁is a function of (e.g., proportional to) the pulse width T₁. Inaddition, the PW₂ is the same length as the burst period B₂ within 10%;and the first pulse voltage V₂ is a function of (e.g., proportional to)the pulse width T₂. PW₁ and PW₂ may have widths that deviate from B₁ andB₂ due to circuit phase delays, and the charging and discharging ofvarious circuit elements. However, the input and output lengths arestrongly correlated, with the input burst lengths being used to controlthe output pulse lengths. Load properties will also impact the exactcorrelation between the input burst width and the output pulse width.The flatness of the output pulses may also vary based on the circuitelements selected, and/or may show a natural oscillation/response to theinput pulses that comprise the burst.

In some embodiments, the time between pulses can be any value. In someembodiments, the time between pulses can be on the order of the pulsewidth of an individual pulse.

In some embodiments, the frequency of the pulses within each burst maybe greater than about 1 kHz, 10 kHz, 100 kHz, 1,000 kHz, etc.

FIG. 8C illustrates an example pulser waveform and FIG. 8D illustratesan example high voltage waveform generator output waveform according tosome embodiments. In this example, the input waveforms are inverted incomparison with those shown in FIG. 8A, resulting in inverted outputwaveforms shown in FIG. 8D. In this example, the pulse widths of theoutput pulses PW₁ and PW₂ are substantially similar to the burst periodB₁ and B₂. The waveforms shown in FIGS. 9, 10, and 11 can likewise beinverted. The flatness of the output pulses may also vary based on thecircuit elements selected, and/or may show a naturaloscillation/response to the input pulses that comprise the burst.

FIG. 9A illustrates an example waveform produced by the pulser and FIG.9B illustrates an example high voltage waveform generator outputwaveform according to some embodiments. In this example, the first twopulses of the first burst of the pulser output as shown in FIG. 9A areshorter than the other pulses within the burst. This results in anoutput pulse that slowly ramps up to V₂ or V₁ as shown in FIG. 9B. Thismay be done to limit the peak output current and/or energy from thepulser.

The output waveforms shown in FIGS. 8B, 8D, and 9B may be referred to asa form of ‘bi-level’ control, where the intent is to apply a series of 1or more output pulses of one voltage alternating with a series of one ormore output pulses with a different voltage. For example, this may allowhigh energy ions to interact with a surface/material, followed by lowenergy ions interacting with a surface/material.

FIG. 10A illustrates an example waveform produced by the pulser and FIG.10B illustrates an example high voltage waveform generator outputwaveform according to some embodiments. In this example, the pulse widthof each pulse within a burst increases linearly as shown in FIG. 10Aresulting in an output waveform voltage that similarly decreaseslinearly as shown in FIG. 10B.

FIG. 11A illustrates an example waveform produced by the pulser and FIG.11B illustrates an example high voltage waveform generator outputwaveform according to some embodiments. In this example, three burstshaving three different burst widths and the pulses within each bursthave different pulse widths as shown in FIG. 11A. This results in threeoutput pulses with three different pulse widths and different voltagesas shown in FIG. 11B.

The shape of the output waveform can be dictated by the pulse width ofeach pulse within a burst and/or the burst width. Any shape of outputwaveform may be produced by varying these parameters. Such shapes may berepeated and interleaved with any other set of output pulse shapes, andmay be done so in a repetitive manner. In some embodiments, the shape ofthe output waveform can be controlled/set by varying the voltage of theindividual pulses. Varying the pulse width may vary the pulse voltage aswell.

In some embodiments, multiple nanosecond pulsers may be phased together.For example, the nanosecond pulser 105 may include one or more pulsersphased together in parallel. This may, for example, generate outputpulses from the waveform generator at higher frequencies.

FIG. 12 illustrates example waveforms within various circuit elements ofa high voltage waveform generator according to some embodiments. Thewaveforms shown in FIG. 12 relate to the components shown in FIG. 7.

FIG. 13 and FIG. 14 illustrates example waveforms within various circuitelements of a high voltage waveform generator according to someembodiments. The waveforms shown in FIG. 12 relate to the componentsshown in FIG. 7.

In some embodiments, a high voltage waveform generator may use real timefeedback to adjust the output voltage of an output waveform. Forexample, a circuit can determine that the voltage of an output waveformis lower than expected, in response the pulse width of the nanosecondpulser may be adjusted to produce the desired output pulse.Alternatively, the number of pulses within a burst may be adjusted,and/or their frequency may be adjusted.

In some embodiments, a plurality of pulsers may be used in a highvoltage waveform generator 750. For example, a first pulser and a secondpulser can be phased together with one or more switches. Linkingtogether these pulses can be done to increase the frequency of thepulses provided to the load. In some embodiments, each of the pulsersmay produce a different drive voltage.

In some embodiments, the resistor at the gate of one or more MOSFETswithin the pulser may be selected to enable a working range between highlevels and low levels in bi-level operation. In some embodiments, theresistor at the gate of one or more MOSFETs may provide short circuitprotection. In some embodiments, different gate voltages may be appliedto one or more MOSFETs within the pulser.

In some embodiments, the turn on time of one or more switches within thenanosecond pulser 105 may result in lower output voltage from the pulserwhen the pulse width is less than the rise time. This is illustrated inFIG. 15C. V₃, for example, may be 5 kV or greater and V₄, for example,may be greater than 200 volts.

A pulser may include a high voltage DC input and a low voltage DCwaveform for controlling the solid-state switches or gate voltage. Thewaveform shown in FIG. 15A shows the gate voltage with two bursts eachhaving a burst period, B₁ and B₂, and the pulses within each bursthaving a different pulse width. The waveform in FIG. 15B shows examplepulses produced by the pulser (e.g., the voltage across R1 in FIG. 7).The voltage of the pulses within the first burst are at V₁ and thepulses within the second burst are at V₂. The pulse voltages in thesecond burst are lower because the gate voltage pulse widths areshorter. Specifically, the gate voltage pulses are sufficiently shortthat the pulser switches do not have time to fully turn on, (e.g., reachtheir peak output voltage) before the pulse switches are turned back offby the gate input pulse. The waveform in FIG. 15D is the voltage acrossthe switch in the pulser (e.g., switch S1 in FIG. 7). The switches aregated on for a sufficiently short period that the voltage across theswitch is never able to fall to the low level that it would normally befor a switch fully turned on and in full conduction. The resultingoutput waveform shown in FIG. 15C has two voltage levels. The secondvoltage level is a function of the pulse width of the gate voltagewaveform (FIG. 15A). Because the pulse widths of the second pulses areshorter than the switch rise time, or the switch turn-on time, or theswitch time needed to reach full conduction, lower voltage pulses areproduced by the pulser. The second voltage level in FIG. 15C is afunction of the pulse width and the voltage produced by the pulser shownin FIG. 15B. The gate resistance of one or more switches in the pulsermay determine the rise time and voltage of the pulses provided by thepulser.

In some embodiments, the output voltage shown in FIG. 15C is a functionof single pulses shown in FIG. 15A. In some embodiments, output voltagecontrol is provided using the switches to control output voltage. Someembodiments may enable very fast, nanosecond timescale, output voltagemodulation, at bi-level voltage output. This can, for example, allow forfast voltage modulation (e.g., greater than 1 MHz).

Numerous specific details are set forth herein to provide a thoroughunderstanding of the claimed subject matter. However, those skilled inthe art will understand that the claimed subject matter may be practicedwithout these specific details. In other instances, methods, apparatusesor systems that would be known by one of ordinary skill have not beendescribed in detail so as not to obscure claimed subject matter.

Some portions are presented in terms of algorithms or symbolicrepresentations of operations on data bits or binary digital signalsstored within a computing system memory, such as a computer memory.These algorithmic descriptions or representations are examples oftechniques used by those of ordinary skill in the data processing artsto convey the substance of their work to others skilled in the art. Analgorithm is a self-consistent sequence of operations or similarprocessing leading to a desired result. In this context, operations orprocessing involves physical manipulation of physical quantities.Typically, although not necessarily, such quantities may take the formof electrical or magnetic signals capable of being stored, transferred,combined, compared or otherwise manipulated. It has proven convenient attimes, principally for reasons of common usage, to refer to such signalsas bits, data, values, elements, symbols, characters, terms, numbers,numerals or the like. It should be understood, however, that all ofthese and similar terms are to be associated with appropriate physicalquantities and are merely convenient labels. Unless specifically statedotherwise, it is appreciated that throughout this specificationdiscussions utilizing terms such as “processing,” “computing,”“calculating,” “determining,” and “identifying” or the like refer toactions or processes of a computing device, such as one or morecomputers or a similar electronic computing device or devices, thatmanipulate or transform data represented as physical electronic ormagnetic quantities within memories, registers, or other informationstorage devices, transmission devices, or display devices of thecomputing platform.

The system or systems discussed herein are not limited to any particularhardware architecture or configuration. A computing device can includeany suitable arrangement of components that provides a resultconditioned on one or more inputs. Suitable computing devices includemultipurpose microprocessor-based computer systems accessing storedsoftware that programs or configures the computing system from a generalpurpose computing apparatus to a specialized computing apparatusimplementing one or more embodiments of the present subject matter. Anysuitable programming, scripting, or other type of language orcombinations of languages may be used to implement the teachingscontained herein in software to be used in programming or configuring acomputing device.

Embodiments of the methods disclosed herein may be performed in theoperation of such computing devices. The order of the blocks presentedin the examples above can be varied—for example, blocks can bere-ordered, combined, and/or broken into sub-blocks. Certain blocks orprocesses can be performed in parallel.

The use of “adapted to” or “configured to” herein is meant as open andinclusive language that does not foreclose devices adapted to orconfigured to perform additional tasks or steps. Additionally, the useof “based on” is meant to be open and inclusive, in that a process,step, calculation, or other action “based on” one or more recitedconditions or values may, in practice, be based on additional conditionsor values beyond those recited. Headings, lists, and numbering includedherein are for ease of explanation only and are not meant to belimiting.

The terms “first” and “second” are not necessarily used to identify theabsolute or very first or second of sequence of items. Rather, theseterms are used solely to label an item and a different or subsequentitem unless the meaning is clear that the terms are meant to specify aspecific order or absolute position. The order of the items labeled with“first” and “second” may or may not be the absolute order and/or mayinclude other items in between.

While the present subject matter has been described in detail withrespect to specific embodiments thereof, it will be appreciated thatthose skilled in the art, upon attaining an understanding of theforegoing, may readily produce alterations to, variations of, andequivalents to such embodiments. Accordingly, it should be understoodthat the present disclosure has been presented for purposes of examplerather than limitation, and does not preclude inclusion of suchmodifications, variations and/or additions to the present subject matteras would be readily apparent to one of ordinary skill in the art.

That which is claimed:
 1. A high voltage waveform generator comprising: a generator inductor; a high voltage nanosecond pulser electrically and/or inductively coupled with the generator inductor, the high voltage nanosecond pulser configured to charge the generator inductor with: a first pulse burst comprising a first plurality of high voltage pulses, each pulse of the first plurality of pulses having a pulse width, the first pulse burst having a first burst period; and a second pulse burst comprising a second plurality of high voltage pulses, each pulse of the second plurality of pulses having a pulse width, the second pulse burst having a second burst period; and a plasma coupled with the nanosecond pulser and the generator inductor, the voltage across the plasma varying according to: a first plasma pulse having a first output pulse width and a first output voltage, the first output pulse width being substantially equal to the first burst period and the first output voltage being substantially proportional to a pulse width of each of the pulses of the first plurality of pulses, and a second plasma pulse having a second output pulse width and a second output voltage, the second output pulse width being substantially equal to the second burst period and the second output voltage being substantially proportional to a pulse width of each of the pulses of the second plurality of pulses.
 2. The high voltage waveform generator according to claim 1, wherein either or both the first pulse burst and the second pulse burst has an amplitude greater than 500 V.
 3. The high voltage waveform generator according to claim 1, wherein either or both the first plasma pulse and the second plasma pulse has an amplitude greater than 500 V.
 4. The high voltage waveform generator according to claim 1, wherein the second pulse burst has an amplitude that is different than the amplitude of the first pulse burst.
 5. The high voltage waveform generator according to claim 1, wherein the amplitude of one or more of the first plurality of high voltage pulses is different than amplitude of one or more of the other first plurality of high voltage pulses.
 6. The high voltage waveform generator according to claim 1, wherein the voltage of the first plasma pulse is different than the voltage of the second plasma pulse.
 7. The high voltage waveform generator according to claim 1, further comprising a pulldown resistor electrically and/or inductively coupled with the generator inductor and the high voltage nanosecond pulser.
 8. The high voltage waveform generator according to claim 1, further comprising a transformer.
 9. The high voltage waveform generator according to claim 1, wherein the first burst period and/or the second burst period is less than about 50 ms.
 10. The high voltage waveform generator according to claim 1, wherein either or both the first plasma pulse and the second plasma pulse establish a potential within the plasma.
 11. The high voltage waveform generator according to claim 1, wherein either or both the first plasma pulse and the second plasma pulse accelerate ions within the plasma.
 12. The high voltage waveform generator according to claim 1, wherein either or both the first plurality of pulses and/or the second plurality of pulses have a frequency greater than about 50 kHz.
 13. The high voltage waveform generator according to claim 1, wherein at least one pulse of the first plurality of pulses has a pulse width and/or at least one pulse of the second plurality of pulses has a pulse width less than 500 ns.
 14. The high voltage waveform generator according to claim 1, wherein the generator inductor comprises stray inductance.
 15. The high voltage waveform generator according to claim 1, wherein the generator inductor has an inductance less than about 20 μH.
 16. The high voltage waveform generator according to claim 1, wherein the peak output power is greater than 10 kW.
 17. The high voltage waveform generator according to claim 1, wherein the plasma is substantially capacitive in nature.
 18. A method for generating high voltage waveforms within a plasma, the method comprising: generating a first pulse burst comprising a first plurality of high voltage pulses, each pulse of the first plurality of pulses having a pulse width and a voltage greater than 500 V, the first pulse burst having a first burst period; charging a generator inductor with the first pulse burst; outputting a first output pulse having a first output pulse width and a first output voltage, the first output pulse width being substantially equal to the first burst period and the first output voltage being substantially proportional to the pulse width of each of the first plurality of pulses; generating a second pulse burst comprising a plurality of high voltage pulses, each pulse of the second plurality of pulses having a pulse width, the second pulse burst having a second burst period; charging a generator inductor with the second pulse burst; and outputting a second output pulse having a first output pulse width and a second output voltage, the second output pulse width being substantially equal to the second burst period and the second output voltage being substantially proportional to the pulse width of each of the second plurality of pulses.
 19. The method according to claim 18, wherein the first output pulse and the second output pulse are applied to a plasma.
 20. The method according to claim 18, wherein the first output pulse and the second output pulse accelerate ions within a plasma.
 21. The method according to claim 18, wherein charging the generator inductor comprises passing energy through the generator inductor.
 22. The method according to claim 18, wherein at least one pulse of the first plurality of pulses has a pulse width and/or at least one pulse of the second plurality of pulses has a pulse width less than 500 ns.
 23. The method according to claim 18, wherein at least one pulse of the first plurality of pulses has a different pulse width and/or at least one pulse of the second plurality of pulses has a different pulse width.
 24. The method according to claim 18, wherein the amplitude of one or more of the first plurality of pulses is different than amplitude of one or more of the other first plurality of pulses.
 25. A high voltage waveform generator comprising: a generator inductor; a high voltage nanosecond pulser having one or more solid state switches electrically coupled with the generator inductor, the high voltage nanosecond pulser configured to produce a pulse burst having a burst period, the pulse burst comprising a plurality of pulses having different pulse widths; and a plasma electrically coupled with the high voltage nanosecond pulser and the generator inductor, the voltage across the plasma having an output pulse with a pulse width substantially equal to the burst period and the voltage across the plasma varying in a manner that is substantially proportional with the pulse widths of the plurality of pulses.
 26. The high voltage waveform generator according to claim 25, wherein at least a subset of the plurality of pulses have pulse widths with increasingly larger pulse widths and the absolute value of the voltage across the plasma increases.
 27. The high voltage waveform generator according to claim 25, wherein at least a subset of the plurality of pulses have pulse widths with decreasingly smaller pulse widths and the absolute value of the voltage across the plasma decrease.
 28. The high voltage waveform generator according to claim 25, wherein the voltage across the plasma accelerates ions within the plasma. 